In 2372, while on a diplomatic mission to negotiate a trade agreement between the Karemma and the Ferengi, the Defiant was for the first time capable of repelling enemy fire from Jem'Hadar fighters with its shields. (DS9: "Starship Down") The Dominion did not become aware of the Federation shield upgrades until the Second Battle of Deep Space 9 in 2373, when Dominion forces were surprised to see Deep Space 9's shields holding under phased polaron beam fire. The station's shields were eventually penetrated, but only after a protracted battle that saw the polaron beams reduced in effectiveness to the level of any other energy weapon (DS9: "Call to Arms").

According to the Star Trek: Deep Space Nine Technical Manual (page 91), the shields of Deep Space 9 were augmented with power supply upgrades and predictive-adaptive shield control routines. Nine capacitance banks boosted shield strength with reserve energy. The deflector shield strength increased from a field strength of 450.5 megawatts to 2.6 gigawatts for up to 32 second bursts at a time.